A fuel cell system is a system which generates electric power by an electrochemical reaction between fuel and an oxidizing agent supplied to a fuel cell from the outside of the fuel cell system, recovers heat generated by the reaction, stores the heat as hot water, and effectively utilizes the hot water for heat supply to the outside of the fuel cell system. Specifically, cooling water is supplied to the fuel cell, and the supplied cooling water carries out heat exchange in the fuel cell to be heated and then discharged from the fuel cell. Then, the discharged cooling water exchanges heat with a heat medium (water) in a heat exchanger to be cooled down, and again, is supplied to the fuel cell.
Meanwhile, the heat medium which has carried out the heat exchange in the heat exchanger is further heated by an electric heater and is stored in a hot water tank. At this time, the problem arises where dissolved oxygen in the heat medium becomes bubbles, the bubbles deteriorate the performance of a pump disposed on an exhaust heat recovery passage through which the heat medium flows, and this disturbs control of water delivery.
To solve the above problem, a fuel cell power generating system in which an air release valve is disposed on a circulation passage (exhaust heat recovery passage) is known (see Patent Document 1 for example). In the fuel cell power generating system disclosed in Patent Document 1, since the air release valve is disposed on a hot water circulation passage including the heat exchanger and the fuel cell, the bubbles generated in the circulation passage can be removed.
Patent Document 1: Japanese Laid-Open Patent Application Publication 2003-223913